1. Field of the Invention
This invention relates to a thermal processing unit and a thermal processing method, such as a film-forming processing unit and a film-forming processing method, for an object to be processed such as a semiconductor wafer.
2. Disclosure of the Prior Art
In general, a batch-type of thermal processing unit is mainly used for various thermal processes, for example a film-forming process, to a semiconductor wafer or the like because the batch-type of thermal processing unit can conduct a thermal process to many semiconductor wafers at a time.
In the thermal processing unit, about 70 to 150 semiconductor wafers are supported at a predetermined pitch by a wafer-boat made of quartz. The wafer-boat is housed in a longitudinal cylindrical processing chamber. A processing gas flows upward or downward in the processing chamber. Thus, a predetermined thermal process such as a film-forming process can be conducted to the many semiconductor wafers.
A typical batch-type of thermal processing unit is explained below.
FIG. 21 is a schematic view of a common batch-type of thermal processing unit. As shown in FIG. 21, the batch-type of thermal processing unit 102 includes a processing chamber vessel 108 which has an inside cylinder 104 and an outside cylinder 106. A wafer-boat 110 is housed in a processing space S defined in the inside cylinder 104. The wafer-boat 110 can be inserted into and discharged from the processing space S through a bottom opening of the inside cylinder 104. Many, for example about 150 product wafers Ware placed on the wafer-boat 110 at a predetermined pitch. Then, a predetermined thermal process such as CVD (Chemical Vapor Deposition) is conducted to the wafers W.
A processing gas such as a film-forming gas can be introduced into the processing chamber vessel 108 through a lower portion thereof. Then, the processing gas flows upward in the processing space S of the inside cylinder 104, where is a high temperature area, while reacting with the wafers W. After that, the processing gas turns down and flows downward between the inside cylinder 104 and the outside cylinder 106. Then, the processing gas is discharged outside from an exhaust opening 112. Heaters not shown are arranged at respective zones in a surrounding area of the processing chamber vessel. During the thermal process, the semiconductor wafers W are maintained at a processing temperature, and an inside of the processing chamber vessel is maintained at a processing pressure.
The processing gas introduced into the processing chamber vessel flows upward in a surrounding area of the wafers in a direction in which the wafers are arranged (a vertical direction in FIG. 21). A part of the processing gas flows between neighboring two wafers and reacts with the two wafers by a thermal decomposition. Thus, films can be deposited on the wafers.
In the case of the film-forming process, in order to improve the productivity, it is desired that fine quality films can be formed on wafers at a high film-forming rate, with a high level of film-thickness uniformity within a wafer and with a high level of film-thickness uniformity in wafer to wafer.
In order to raise film-forming rates for various films, it is effective to promote the reactions of the processing gases by raising parameters such as amounts (flow rates) of the supplied processing gases, processing pressures, processing temperatures or the like. However, in order to obtain fine quality films, the above parameters can not be raised over respective limitations. For example, when SiH4 gas is used as a processing gas to form a poly-Si film on a wafer, the film can not have a fine quality if the processing pressure is higher than 1.5 Torr. The reason is that decomposing reactions in the gas phase are promoted too much since the time for which the SiH4 gas passes through the hot processing space S becomes long if the processing pressure is higher than 1.5 Torr.
If the reactions in the gas phase are promoted too much, powdery Si deposits on the wafer to deteriorate the quality of the film. In addition, the powdery Si may turn into particles. Thus, the processing pressure has to be not higher than 1.5 Torr to conduct a fine film-forming process wherein reactions in the gas phase are restrained but decomposing reactions are promoted on the wafer i.e. surface-reactions a remain. Thus, the maximum of the film-forming rate is about 15 xc3x85/min.
This invention is intended to solve the above problems effectively. The object of this invention is to provide a thermal processing unit and a thermal processing method that can not deteriorate a quality of a thermal process but raise a thermal processing rate such as a film-forming rate.
The inventor of the invention has found the following matters. When a processing gas is forcibly caused to pass between neighboring two of a tier-like plurality of semiconductor wafers, the time for which the processing gas passes between them becomes short and reactions in the gas phase are restrained. Thus, even when the processing pressure is high, the reactions in the gas phase can be restrained and the film-forming rate can be raised. Then, this invention has been gotten in shape.
This invention is characterized by a feature wherein a thermal processing unit comprises: a substrate-holder which can support a plurality of substrates in such a manner that the plurality of substrates are arranged at a predetermined pitch; a chamber vessel for housing the substrate-holder, said chamber vessel having an inside being made a vacuum; a gas-introducing slit having a small conductance provided in one part of a peripheral area of the plurality of substrates held by the substrate-holder, said gas-introducing slit extending in a direction in which the plurality of substrates are arranged and supplying a processing gas for a thermal process into the chamber vessel; a gas-absorbing opening having a large conductance provided in another part of the peripheral area of the plurality of substrates held by the substrate-holder, said gas-absorbing opening extending in the direction in which the plurality of substrates are arranged; and a loading mechanism for loading and unloading the substrate-holder into and out of the chamber vessel.
According to the feature, the processing gas is forcibly caused to pass between the substrates because the processing gas flows from the gas-introducing slit having the small conductance to the gas-absorbing opening having the large conductance. Then, the staying time for which the processing gas passes and stays between the substrates becomes short. Thus, when the thermal process is a film-forming process, even when the processing pressure is high, reactions in the gas phase are so restrained that film-forming reactions by surface-reactions are main, i.e., the film-forming process can be conducted at a high film-forming rate.
Preferably, the chamber vessel has an inside cylinder for housing the substrate-holder and an outside cylinder surrounding the inside cylinder, and the gas-introducing slit and the gas-absorbing opening are formed in the inside cylinder.
Preferably, the gas-introducing slit is formed along one part of a side wall of the chamber vessel, and the gas-absorbing opening is formed by outward denting another part of the side wall of the chamber vessel.
Preferably, the gas-introducing slit is divided into a plurality of zone-slits which respectively correspond to a plurality of zones divided in the direction in which the plurality of substrates are arranged.
According to the feature, the processing gas can be supplied substantially uniformly through the plurality of zone-slits which respectively correspond to the plurality of zones divided in the direction in which the plurality of substrates are arranged.
In the case, preferably, the plurality of zone-slits are respectively connected to a plurality of flow-controllers which respectively correspond to the plurality of zones.
Preferably, each of the plurality of zone-slits is divided into a plurality of slit-elements which respectively correspond to a plurality of peripheral areas of the plurality of substrates.
According to the feature, the processing gas can be supplied substantially uniformly in each of the plurality of substrates.
Preferably, the substrate-holder has board-members coming in contact with portions of peripheries of the plurality of substrates on both sides of the gas-absorbing opening, said board-members having arc sections and predetermined thicknesses extending from the portions of peripheries of the plurality of substrates in a radial direction of the plurality of substrates respectively.
According to the feature, the board-members can function as baffle plates to prevent the processing gas from flowing outside of the substrates and to guide the processing gas between the substrates. Thus, for example, the film-forming rate can be raised even when the volume of the supplied processing gas is small.
In addition, this invention is characterized by a feature wherein a thermal processing method comprises: a step of supporting a plurality of substrates in such a manner that the plurality of substrates are arranged at a predetermined pitch; and a step of supplying a processing gas for a thermal process from a gas-introducing slit to a gas-absorbing opening and causing the processing gas to pass between any neighboring two of the plurality of substrates, said gas-introducing slit having a small conductance provided in one part of a peripheral area of the plurality of substrates, and extending in a direction in which the plurality of substrates are arranged, said gas-absorbing opening having a large conductance provided in another part of the peripheral area of the plurality of substrates, and extending in the direction in which the plurality of substrates are arranged.
Preferably, the gas-introducing slit is divided into a plurality of zone-slits which respectively correspond to a plurality of zones divided in the direction in which the plurality of substrates are arranged.
Preferably, a volume of the processing gas for the thermal process supplied into each of the plurality of zone-slits is controlled independently.
Preferably, the volume of the processing gas for the thermal process supplied into each of the plurality of zone-slits is controlled in such a manner that the volume is larger when a zone-slit is nearer to a discharging opening connected to the gas-absorbing opening.
In addition, this invention is characterized by a feature a film-forming processing method comprises: a step of supporting a plurality of substrates in such a manner that the plurality of substrates are arranged at a predetermined pitch; and a step of supplying a processing gas for a film-forming process from a gas-introducing slit to a gas-absorbing opening and causing the processing gas to pass between any neighboring two of the plurality of substrates, said gas-introducing slit having a small conductance provided in one part of a peripheral area of the plurality of substrates, and extending in a direction in which the plurality of substrates are arranged, said gas-absorbing opening having a large conductance provided in another part of the peripheral area of the plurality of substrates, and extending in the direction in which the plurality of substrates are arranged.
Preferably, the gas-introducing slit is divided into a plurality of zone-slits which respectively correspond to a plurality of zones divided in the direction in which the plurality of substrates are arranged.
Preferably, a volume of the processing gas for the film-forming process supplied into each of the plurality of zone-slits is controlled independently.
Preferably, the volume of the processing gas for the film-forming process supplied into each of the plurality of zone-slits is controlled in such a manner that the volume is larger when a zone-slit is nearer to a discharging opening connected to the gas-absorbing opening.